I download the latest version of TCP Optimizer.
Then, set connection speed 512kpbs, Modify All network adapter and PPOE tick.
Optimal setting. After resetting pc. I noticed my connection slow down.
Also, I noticed start up being so long.

SpeedGuide.net TCP Analyzer Results
Tested on: 2012.02.17 02:03
IP address: 115.132.xxx.xxx
Client OS/browser: Windows XP (Chrome 17.0.963.56)

TCP options string: 020405ac0103030101010402
MSS: 1452
MTU: 1492
TCP Window: 65536 (NOT multiple of MSS)
RWIN Scaling: 1 bits (2^1=2)
Unscaled RWIN : 32768
Recommended RWINs: 63888, 127776, 255552, 511104, 1022208
BDP limit (200ms): 2621kbps (328KBytes/s)
BDP limit (500ms): 1049kbps (131KBytes/s)
MTU Discovery: ON
TTL: 52
Timestamps: OFF
IP ToS: 00000000 (0)

Using windows XP , 32 Bit, SP3